Regions of the pea Lhcb1*4 promoter necessary for blue-light regulation in transgenic Arabidopsis.

Pea (Pisum sativum) and Arabidopsis contain similar, if not identical, blue-light (BL)-responsive systems that alter expression of specific members of the Lhcb (light-harvesting chlorophyll-binding) gene family. In both plants a single, short pulse of low-fluence BL (threshold = 10(-1) micromol m-2) causes an increase in the rate of transcription from specific members of the Lhcb gene family in etiolated seedlings. Constructs of the BL-regulated pea Lhcb1*4 promoter (PsLhcb1*4) were created, which altered sequences previously implicated in light responses, deleted the 5'-promoter sequence, or removed the 5'-untranslated region. These constructs were tested for BL induction in transgenic Arabidopsis. The PsLhcb1*4 promoter deletions to -150 bp maintained normal fluence response, time course, and reciprocity characteristics. The 5'- untranslated region contained enhancer elements, but was not necessary for BL induction. The -95 to +2 promoter was capable of responding to BL, whereas sequences from -50 were not. Promoters that lack conserved light-regulatory elements or sequences directly implicated in phytochrome and circadian responses retained BL activity, suggesting that the low-fluence BL response utilizes regions of the promoter independent of those that modulate the phytochrome and circadian responses.